Conventionally, as a planar light source device that illuminates a liquid crystal panel, a so-called illumination device of direct type, which is disposed right under a rear surface of the liquid crystal panel, is proposed. As a light source of such an illumination device, it is possible to use a tube-like light source (e.g., cold-cathode tube lamp) as in patent documents 1 to 3 or use a point light source (e.g., LED (light emitting diode) as in a patent document 4. Especially, an LED is advantageous in longevity and low power consumption, and in recent years, many LEDs are used as light sources of illumination devices.
In the meantime, when humans watch a screen of a liquid crystal panel, they watch more carefully the screen center than the screen peripheral. Because of this, in a case of using LEDs as the light source, even if the disposition density of the LEDs is made low at the peripheral portion, visual brightness unevenness is not conspicuous. As described above, by partially changing the disposition density of the LEDs, it is possible to secure the brightness of a necessary region (screen center) and achieve low cost by reducing the number of LEDs mounted.
When changing partially the disposition density of the LEDs, in the patent document 4, as shown in FIG. 25, LED boards 102 mounting a plurality of LEDs 101 are disposed in parallel, and disposition intervals of the LED boards 102 are partially changed. Specifically, in a central portion Rc in an arrangement direction of the LED boards 102, the interval of neighboring LED boards 102 is made narrow, while in an outside peripheral portion Rp with respect to the central portion Rc in the arrangement direction of the LED boards 102, the interval of neighboring LED boards 102 is made wide. As described above, it is conceivable that by adjusting the interval of the LED boards 102 to change partially the disposition density of the LEDs, it is also possible to easily deal with a size change of an illumination device 100.
Besides, in the illumination device in the patent document 4, a reflection sheet 103 is disposed on a bottom plate (mounting surface) of a backlight chassis where the LED board 102 is mounted. The reflection sheet 103 has an opening portion for exposing the LED 101 and is disposed on the bottom plate to cover the LED board 102. An edge portion 103a of the reflection sheet 103 rises obliquely from the bottom plate. As described above, by disposing the reflection sheet 103, even if the LED 101 is not disposed on a peripheral portion of the bottom plate, it is possible to illuminate a screen peripheral portion of a liquid crystal panel by means of light that is emitted from the LED 101 and reflected by the edge portion 103a of the reflection sheet 103. Accordingly, it is possible to achieve low cost by further reducing the number of LEDs 101 mounted.